The research plan involves a three-pronged approach to development and plasticity of the hamster visual system, including anatomy, physiology and behavior. The long-range goal of the anatomical studies is to explain and predict the formation of anomalous pathways after early brain damage in terms of perturbations of a limited number of normal developmental factors that contribute to the formation of selective neuronal connections in the CNS. Two such factors we will focus on are: growing axons compete for limited territory and they attempt to form a particular number connections. Their relative roles will be assessed by studying the morphology of single optic arborizations under conditions produced by early lesions that either incease or decrease the available territory in the superior colliculus. In midbrain and thalamic areas of the visual system we will evaluate the hypothesis that precise neuronal connections are attained through a process of progressive remodelling of initially more widespread axonal projections, experiments which will bear on the question of whether such normal developmental reorganization is the basis for the greater plasticity observed in younger animals in response to brain damage. In a new line of work, altered visual cortical projectiors will be looked for after neontal section of the corpus callosum, a potential animal model for agenesis of the callosum in man in which there is much functional sparing. Collaborative work will be done in human brains using a new degeneration stain that may eventually allow us to detect anomaulous pathways in man. The functional impact of altered connections in the superior colliculus and pretectum will be studied using several new tests of visumotor function. In extending previous work that correlated disarranged and rearranged topography of retinal projections with misdirected and uncoordinated visuomotor responses, we are now exploring the possibility that an abnormally high density of optic tract projections can underly supernormal resonsivity. Finally, a major new thrust of our work seeks to carry the functional studies to the cellular level with electrophysiological unit analysis.